What is the difference between a postdeadline submission and a regular submission?

Postdeadline submissions are not an opportunity to submit a paper after the published deadline, but are intended to provide those with late-breaking work an opportunity to submit that work for consideration. Postdeadline submissions should describe new and significant material in rapidly advancing areas. A limited number of postdeadline submissions will be selected for presentation, and only those papers judged to be excellent and compelling in their timeliness will be accepted.